1. Field of the Invention
The present invention relates to a method of blanking an element for a belt for use in a continuously variable transmission.
2. Description of the Related Art
Elements for belts for use in continuously variable transmissions comprise a body and a head joined to the body by a neck. A plurality of such elements are assembly as follows: The elements are stacked, with their faces held closely against backs of adjacent ones, into an annular shape, and endless rings are mounted in recesses defined between the bodies and the heads to bind the elements together in the annular form, thus producing a belt for use in a continuously variable transmission. The bodies of the elements are positioned on an inner circumferential side of the annular belt and have opposite side edges located for contact with pulleys of the continuously variable transmission.
An element of the type described above is blanked out of a metal sheet by pressing a punch that is complementary in shape to the element against the metal sheet that is placed on the die of a press. Since the opposite side edges of the body which are positioned for contact with pulleys of the continuously variable transmission need to be sheared to shape highly accurately, cutting edges of the die and the punch are spaced from each other by a gap that is set to a relatively small distance, which is about 0 to 1% of the thickness of the element, along the outer profile of the element. The die and punch are capable of producing a highly accurate element with a transversely wide sheared surface along the blanked edges of the element.
As shown in FIG. 5(b) of the accompanying drawings, the element thus produced has a burr f formed on an edge corner on the side of the element that is pressed by the punch and rising continuously from a sheared surface d. The element that has been blanked is processed by barrel polishing to remove the burr f.
According to the deburring process based on the barrel polishing, however, the medium may not enter fully into the recesses between the body and the head, possibly failing to remove the burr sufficiently from the opposite sides of the neck that are positioned deeply in the recesses. Any burrs remaining on the opposite sides of the neck tend to contact and hence damage the endless rings which is mounted in the recesses between the body and the head.
It has heretofore been known in the art to a dedicated deburring device for removing the burrs from the opposite edges of the neck. The deburring device has a polishing belt which is inserted into the recesses between the body and the head of each individual element to deburr the opposite edges of the neck.
The deburring device is liable to increase the manufacturing cost of the element, increase the number of steps required to produce the element, and reduce the efficiency with which to produce the element.
It is therefore an object of the present invention to provide a method of blanking an element to shape highly accurately for preventing endless rings, to be combined with elements, from being damaged by contact therewith, so that the cost and number of steps required by deburring the element can be reduced.
According to the present invention, there is provided a method of blanking an element for a belt for use in a continuously variable transmission which is produced by stacking a plurality of plate-shaped elements each having a body with opposite side edges positioned for contact with a pulley of the continuously variable transmission and a head joined to the body by a narrower neck, and inserting endless rings into recesses defined between the body and the neck by the neck. In the method, an element is blanked out of a metal sheet with a press having a die and a punch. The die and the punch have respective cutting edges, the cutting edge of the punch being more widely spaced from the cutting edge of the die in a range of the element which includes edges of the neck, edges of the head contiguous to the edges of the neck and close to the neck, and edges of the body contiguous to the edges of the neck and close to the neck, than in another range of the element.
When the element is blanked out of the metal sheet by the punch and the die, the edges of the neck, the edges of the head, and the edges of the body are formed of a sheared surface in a transverse direction of the edges and a ruptured surface contiguous to the sheared surface, and a burr is formed next to the ruptured surface in a position out of contact with the endless rings.
When the element is blanked out of the metal sheet by the coaction of the punch and the die, a shear droop, a sheared surface, and a ruptured surface are successively formed in the transverse direction from the die toward the punch on the blanked edge of the element, and a burr is formed contiguous to the ruptured surface along the side wall of the punch. If the distance between the cutting edge of the die and the cutting edge of the punch is relatively small, the extent of the shearing surface is increased and the extents of the shear droop and the ruptured surface are reduced, resulting in a highly accurate blanked edge with a burr positioned highly closely to the blanked edge of the element. Conversely, if the distance between the cutting edge of the die and the cutting edge of the punch is relatively large, then the extent of the shearing surface is reduced and the extents of the shear droop and the ruptured surface are increased, so that a burr is formed next to the ruptured surface in a position spaced from the blanked edge of the element.
According to the present invention, the distance between the cutting edge of the die and the cutting edge of the punch is partly varied to locate the burr on the edges of the neck, the edges of the head contiguous to the edges of the neck and close to the neck, and the edges of the body contiguous to the edges of the neck and close to the neck, in a position out of contact with the endless rings without lowering the accuracy with which to blank the element.
Specifically, in the range including the edges of the neck, the edges of the head contiguous to the edges of the neck and close to the neck, and the edges of the body contiguous to the edges of the neck and close to the neck, the element is blanked out of the metal sheet by the punch whose cutting edge is widely spaced from the cutting edge of the die. For example, the cutting edge of the punch and the cutting edge of the die are spaced from each other by a distance which is 5 to 10% of the thickness of the element in the range of the element which includes the edges of the neck, the edges of the head, and the edges of the body.
With this arrangement, a larger ruptured surface is formed on the edges of the neck, the edges of the head contiguous to the edges of the neck and close to the neck, and the edges of the body contiguous to the edges of the neck and close to the neck, than on other blanked edges. Thus, the burr may easily be formed in a position on one side of the element out of contact with the endless rings.
The burr which is formed on the edges of the neck, the edges of the head contiguous to the edges of the neck and close to the neck, and the edges of the body contiguous to the edges of the neck and close to the neck is sufficiently exposed on one side of the element. When the element is deburred by barrel polishing, the medium used in the barrel polishing is brought into sufficient contact with the burr for thereby easily removing the burr. Consequently, it is not necessary to deburr the element with a conventional dedicated deburring device, and the element can be manufactured with a reduced cost. Inasmuch as the burr is formed in a position out of contact with the endless rings, the endless rings will be prevented from damage even if the removal of the burr by the barrel polishing is not sufficient.
The cutting edge of the punch and the cutting edge of the die should preferably be spaced from each other by a distance which is 0 to 1% of the thickness of the element in the other range of the element. With this distance setting, it is possible to form a sheared surface which is wide in the transverse direction of the element on opposite side edges of the body for contact with pulleys of the continuously variable transmission. As a result, a highly accurate element for a belt for use in a continuously variable transmission can be manufactured.
The above and other objects, features, and advantages of the present invention will become apparent from the following description when taken in conjunction with the accompanying drawings which illustrate a preferred embodiment of the present invention by way of example.